Mould tool and method for resin transfer moulding

ABSTRACT

A mould tool for use in resin transfer moulding operations is provided, the tool comprising one or more shape-defining portions which together define the shape of a component to be manufactured within the tool, and an inlet path for allowing resin to be injected into the mould tool. The mould tool further comprises at least one bleed cavity and a removable closure member, the closure member being capable of closing the bleed cavity and, in use, substantially sealing the bleed cavity to prevent fluid egress from the bleed cavity. A method of resin transfer moulding is also provided. The method comprises at least the steps of: Providing a mould tool having at least one resin injection inlet, at least one bleed cavity and a closure member, the closure member being capable of closing the bleed cavity and, in use, substantially sealing the bleed cavity to prevent fluid egress from the bleed cavity; Placing a pre-formed component in the mould tool and sealing the bleed cavity; Applying a vacuum to an inlet to remove air from the mould tool; Injecting resin through an inlet into the mould tool, any remaining air being forced into the closed bleed cavity by the resin; Heating the mould tool to cure the resin.

This application is the US national phase of international applicationPCT/GB02/04978 filed in English on 1 Nov. 2002, which designated the US.PCT/GB02/04978 claims priority to GB Application No. 0127154.3 filed 13Nov. 2001. The entire contents of these applications are incorporatedherein by reference.

The present invention relates to the manufacture of composite structuresand more particularly to the field of Resin Transfer Moulding (RTM).

A traditional way of producing composite structures involvesmanufacturing carbon fibre fabric, impregnating this with resin to makecarbon fibre sheets, and then laying up the pre-impregnated carbon fibresheets over a mould tool before heating the mould tool and sheets tocure the resin and form the structure. In applications where it is vitalthat the resultant structure must have a uniform thickness, thetraditional method using pre-impregnated carbon fibre sheets is notsufficiently accurate. The thickness of the sheets may not be uniform tostart with, and the resin may not flow evenly during curing. Thesefactors can lead to the structure being outside the tolerance limit forclose tolerance items.

Resin Transfer Moulding (RTM) is becoming a preferred method ofmanufacturing composite structures where tight tolerances are required.The pre-impregnated carbon fibre sheets are not used in RTM. Instead acarbon fibre fabric is partially impregnated or coated with resin, andseveral layers of partially impregnated or coated fabric are laid up ona pre-form tool before being pre-formed at approximately 100 C in avacuum to produce a pre-form structure. This pre-form structure is thenplaced in a RTM mould tool, which is a closed mould tool suitable forinjection moulding. A vacuum is first applied to draw out air, and thena resin is injected into the mould. The mould tool is simultaneouslysubjected to heat for curing the resin, and pressure for ensuring themould tool remains closed, thereby allowing the resin to cure to producethe composite structure. The mould is then opened and the compositestructure removed.

During the resin injection process, a resin bleed is usually carried outto flush out any remaining pockets of air through one or more open bleedpoints. It is necessary that the air be flushed out, otherwise parts ofthe structure will contain air pockets instead of resin and will beweaker than expected. Current RTM processes have several disadvantages,namely: It is difficult to specify and control the resin bleed process,as it usually involves operators observing air bubbles in bleed pipes.This requires judgement and experience from the operators, and precisespecifications from the manufacturers. Special control equipment isusually required. Furthermore, resin is wasted during the bleed process.In cases where the operators are not sure whether the air pockets havebeen removed or not, they will continue to bleed the resin until theyare certain that no significant amount of air remains. A significantamount of resin is wasted in this way. Also, due to the somewhatsubjective nature of establishing when the air pockets have beenexpelled, each component can have slightly different characteristics.

The present invention seeks to provide a RTM mould tool and method ofuse thereof which eliminates the need to specify or control a resinbleed operation during resin injection, and which reduces the amount ofresin wasted in the RTM process. Improved process control and productrepeatability are also sought.

According to the present invention in one aspect thereof there isprovided a mould tool for use in resin transfer moulding operations, thetool comprising one or more shape-defining portions which togetherdefine the shape of a component to be manufactured within the tool, andan inlet path for allowing resin to be injected into the mould tool,wherein the mould tool further comprises at least one bleed cavity and aremovable closure member, the closure member being capable of closingthe bleed cavity and, in use, substantially sealing the bleed cavity toprevent fluid egress from the bleed cavity, and having a flat outersurface to enable the member to fit between the shape-defining portionsof the mould tool and a force exerting platen of a press.

The closure member acts as an intermediate portion to protect the mouldtool from the platen and vice versa during the pressing process.

Alternatively, the closure member may be a stopper which, in use,extends into the bleed cavity and acts to seal the bleed cavity. Astopper may be used instead of an intermediate portion where the mouldtool has its own heating and clamping system.

The mould tool is preferably adapted to allow air to be bled from thesame inlet path as the resin is injected through, prior to injection ofthe resin. This means that only one inlet/outlet path needs to beprovided.

A method of resin transfer moulding may comprise at least the steps of:

Providing a mould tool having at least one resin injection inlet, atleast one bleed cavity and a closure member, the closure member beingcapable of closing the bleed cavity and, in use, substantially sealingthe bleed cavity to prevent fluid egress from the bleed cavity;

Placing a pre-formed component in the mould tool and sealing the bleedcavity;

Applying a vacuum to an inlet to remove air from the mould tool;

Injecting resin through an inlet into the mould tool, any remaining airbeing forced into the closed bleed cavity by the resin;

Heating the mould tool to cure the resin.

The resin is preferably injected until the mould tool cannot accommodateany more resin. The vacuum and the resin injection are preferablyapplied to the same inlet. Preferably there are no open inlets oroutlets other than the said inlet for injecting the resin, so that theresin can not leave the mould tool once injected in.

According to the present invention in another aspect thereof there isprovided a method of resin transfer moulding comprising at least thesteps of:

Providing a mould tool having at least one resin injection inlet, atleast one bleed cavity and a closure member, the closure member beingcapable of closing the bleed cavity and, in use, substantially sealingthe bleed cavity to prevent fluid egress from the bleed cavity;

Placing a pre-formed component in the mould tool;

Exerting pressure on the mould tool by means of a press, the platen ofthe press acting on the closure member and transmitting pressuretherethrough to the rest of the mould tool, the closure member acting toclose and seal the bleed cavity;

Applying a vacuum to an inlet to remove air from the mould tool;

Injecting resin through an inlet into the mould tool, any remaining airbeing forced into the closed bleed cavity by the resin;

Heating the mould tool to cure the resin.

The present invention will now be described by way of example only withreference to the following drawings:

FIG. 1 shows a cross section through a prior art RTM mould tool.

FIG. 2 shows a cross section through a RTM mould tool in accordance withthe present invention.

FIG. 3 shows a cross section through a further RTM mould tool inaccordance with the present invention.

Referring now to FIG. 1, a conventional mould tool 1 comprises a firstshape-defining portion 2 and a second shape-defining portion 3. In use,a pre-formed component 4 is placed in the mould tool and the mould toolis placed in a heating press. A vacuum is applied to outlet 6 to drawout air from the mould tool. Following this operation resin is injectedinto inlet 5, until the operator indicates that the resin exiting themould tool from outlet 6 contains no further air bubbles. No furtherresin is then injected into the mould tool and the component is thencured by heating in the press.

FIG. 2 shows a mould tool having a first shape-defining portion 9, asecond shape-defining portion 8 and a closure member in the form of anintermediate portion 10. In use, a pre-formed component 12 is placed inthe mould tool and the mould tool is placed in a heating press. Theintermediate portion 10 is placed so as to close the bleed cavity 13.When pressure is applied to the intermediate portion by the press, theseal 14 that surrounds the bleed cavity 13 makes contact with theintermediate portion 10 and prevents liquid from the bleed cavity fromescaping. A vacuum is then applied to inlet/outlet 11, to remove airfrom the mould tool. Once most of the air has been removed, resin isthen injected into the mould tool via inlet/outlet 11. As resin isinjected into the mould tool, it displaces any air which is left, andthe air is forced upwards into the bleed cavity 13. The air cannotescape out from the bleed cavity 13 because of the seal 14 and theintermediate portion 10. Resin continues to be injected into the mouldtool until it saturates the component and fills the remainder of thebleed cavity. Thus the air is trapped in the bleed cavity by theintermediate portion 10 at the top and the resin at the bottom. Thecomponent is then cured by heating in the press.

The resultant component is then removed from the mould. A small resinslug is left in the bleed cavity of the mould tool. The tool is designedso that this resin slug can be easily removed. As shown in FIG. 2, partof the bleed cavity wall is defined by an annular ring 15, which abutsthe seal 14. The slug is removed by first removing the annular ring 15,which gives easy access to the slug. A new seal 14 is then installed andthe annular ring 15 is put back in place before the next RTM process iscarried out.

FIG. 3 shows a mould tool 16 having a first shape-defining portion 17, asecond shape-defining portion 18, a bleed cavity 19 and a closure memberin the form of a stopper 20. The mould tool 16 has its own heating andclamping system. In use, a pre-formed component 12 is placed in themould tool and the stopper 20 is inserted into the bleed cavity 19 toclose the bleed cavity 19. A seal 21 surrounds the stopper 20 to preventany resin egress from the bleed cavity. A vacuum is then applied to theinlet/outlet 22, to remove air from the mould tool. Once most of the airhas been removed, resin is then injected into the mould tool viainlet/outlet 22. As resin is injected into the mould tool, it displacesany air that is left, and the air is forced into the bleed cavity 19.The air cannot escape from the bleed cavity 19 because of the stopper 20and seal 21. Resin continues to be injected into the mould tool until itsaturates the component and fills the remainder of the bleed cavity 19,trapping the air at the top of the bleed cavity. The component is thencured by heating, and then removed from the mould tool.

Depending on the size and shape of the component to be manufactured,several bleed cavities may be provided. It can be seen that thisinvention significantly reduces the amount of resin necessary for theRTM process, and provides an improved process control and productquality control.

1. A mould tool for use in resin transfer moulding operations, the toolcomprising: two or more shape-defining portions which together definethe shape of a component to be manufactured within the tool; an inletpath for allowing resin to be injected into the mould tool; at least onebleed cavity; and a removable closure member, the closure member forclosing and sealing the bleed cavity to prevent fluid egress from thebleed cavity, said closure member having a flat outer surface to enablethe member to fit between the shape-defining portions of the mould tooland a force exerting platen of a press.
 2. A mould tool as claimed inclaim 1 wherein the closure member has a flat outer surfacesubstantially parallel to an outer surface of the mould tool.
 3. A mouldtool as claimed in claim 1 wherein the closure member is a stopperwhich, in use, extends into the bleed cavity and acts to seal the bleedcavity.
 4. A mould tool as claimed in claim 1 wherein the mould tool isadapted to allow air to be bled from the same inlet path as the resin isinjected through, prior to injection of the resin.
 5. A method of resintransfer moulding comprising at least the steps of: providing a mouldtool having at least one resin injection inlet, at least one bleedcavity and a closure member, the closure member being capable of closingthe bleed cavity and, in use, substantially sealing the bleed cavity toprevent fluid egress from the bleed cavity; placing a pre-formedcomponent in the mould tool; exerting pressure on the mould tool bymeans of a press having a platen, the platen of the press acting on theclosure member and transmitting pressure therethrough to the rest of themould tool, the closure member acting to close and seal the bleedcavity; applying a vacuum to an inlet to remove air from the mould tool;injecting resin through said resin injection inlet into the mould tool,any remaining air being forced into the closed bleed cavity by theresin; and heating the mould tool to cure the resin.
 6. A method ofresin transfer moulding as claimed in claim 5 wherein the vacuum and theresin injection are applied to the same inlet.